This invention relates generally to a fuel injection nozzle. More particularly, the present invention relates to a fuel injection nozzle for an internal combustion engine.
Fuel injectors of the type contemplated by the present invention have a plunger or valve which is lifted from its seat by the pressure of fuel delivered to the injector by an associated high pressure pump in measured charges in timed relation with the associated engine. Representative fuel injector assemblies are described in U.S. Pat. Nos. 3,829,014, 4,205,789, 4,790,055, and 4,938,193.
The improvements in fuel injection nozzles chronicled by the succession of patents identified above, have been performance related and/or manufacturing related. In the present competitive market for these types of devices, the need to reduce the cost of materials and fabrication without compromising performance continues to be a primary factor. Although some of the devices represented by the prior art provided for improvements in materials and fabrication, further improvements are required.
Many internal combustion engines that utilize fuel injection nozzles are found in automotive applications. A fuel injection nozzle provides the path for injecting fuel into the combustion chamber of the internal combustion engine. Extensive analysis of the combustion process reveals that the most efficient injection point (in some cases) is at the top and center of the combustion chamber. In overhead cam engines the area immediately above the combustion chamber is occupied by the overhead cam (or cams) valve assemblies and connecting mechanisms, such as rocker arms, etc. Placement of injector nozzles in the midst of the valve train makes severe constraints on the length, diameter and overall size of the injector nozzle. Consequently, any reduction in size in the injector nozzle component provides improved flexibility of use.
Additionally, the tip of an injector nozzle includes discharge apertures from which pressurized fuel is delivered into the combustion chamber. Typically, the inside surface of the injector nozzle tip forms a valve seat for sealing with the injector valve between injection pulses. This valve seat/valve interface must form a reliable seal over a useful life that will encompass many millions of injection cycles. Materials for injection valves and injection nozzle tips therefore must be extremely tough, durable, i.e. hard materials. Injector nozzle tips are also subjected to high temperatures and pressures present in the combustion chamber. In high output or turbo-charged engines the temperature in the vicinity of the nozzle tip may well exceed 500° F. for sustained periods of time. Materials used for fuel injection valves and nozzle tips must therefore meet the dual requirements of maintaining their toughness over millions of cycles at sustained high temperatures. This has meant the use of specialty alloy steels having high Rockwell hardness and high temperature tempering properties.
Materials having these properties are typically both expensive and notoriously difficult to work with. The result has been that only the critical portions of the fuel injection nozzle were made from the exotic alloy steels, with the balance of the injector nozzle being more conventional steel. Assembly of injector nozzles from multiple parts increases both the cost and complexity of the manufacturing process.